1. Technical Field of the Invention
The present invention generally relates to a mask, a substrate with a light reflecting film, a method for forming a light reflecting film, a method for manufacturing an electro-optical device, an electro-optical device, and an electronic apparatus.
More particularly, the present invention relates to a mask for manufacturing a substrate with a light reflecting film which reduces the occurrence of interference fringes, a substrate with a light reflecting film formed using the mask, a method for forming a light reflecting film, an electro-optical device comprising a substrate with a light reflecting film which reduces the occurrence of interference fringes, and an electronic apparatus comprising a substrate with a light reflecting film which reduces the occurrence of interference fringes.
2. Related Art
As well known to those skilled in the art, a liquid crystal display device is widely used as a display unit for various electronic apparatuses in line with increasing demand for the electronic apparatuses having thin constitutions and low power consumptions. Such a liquid crystal display device generally has a constitution that in a state of enclosing liquid crystal between a pair of glass substrates, the circumferences of the substrates are bound by means of a sealant. In an electronic apparatus having such a liquid crystal display device mounted therein, a protective plate is disposed on the viewing side of the liquid crystal display device, i.e., on the side of the display facing a viewer, in order to protect the liquid crystal display device against any external impacts. The protective plate normally comprises a plate-shaped member made of a material having a light transmittance characteristic, for example, such as transparent plastic.
However, it is difficult to make the surface of the protective plate opposite to the liquid crystal display device completely smooth over its whole surface, with a result that fine concave portions or convex portions are often present on its surface. Consequently, the display quality may be remarkably deteriorated due to the fine concave portions or convex portions on the surface of the protective plate in case that the protective plate is used in the liquid crystal display device.
One of the reasons for the deterioration of the display quality is that the gap between the substrate on the viewing side of the liquid crystal display device and the protective plate has non-uniformity depending on the concave portions or the convex portions on the surface of the protective plate. In other words, interference is generated due to the non-uniformity of the gap between the substrate and the protective plate when the light emitted from the liquid crystal display device is transmitted through the protective plate, with a result that generates interference fringes. Therefore the interference fringes that occur are overlapped with the displayed images, so that display quality may be deteriorated.
A reflection type liquid crystal display device 400 as shown in FIG. 26 is disclosed in Japanese Unexamined Patent Application Publication No. 6-27481, and a hybrid reflecting/transmitting type liquid crystal display device 500 as shown in FIG. 27 is disclosed in Japanese Unexamined Patent Application Publication No. 11-281972. In the aforesaid liquid crystal display devices, a plurality of concave portions or convex portions 404a, 404b (504a, 504b), the height of which are different from each other, are provided in order to decrease the generation of the interference fringes, respectively. Polymer resin films 405 (505) are formed on the concave and convex portions, and continuous wavelike reflecting electrodes 409 (509) are formed on the polymer resin films.
A method for manufacturing a liquid crystal display device having the aforesaid reflecting electrodes is also disclosed, an example of which is shown in FIG. 28. As shown in FIG. 28(a), a resist film 602 is formed over the entire surface of the glass substrate 600. As shown in FIG. 28(b), the resist film 602 is exposed via a pattern 604 comprising a plurality of circles whose diameters are different from one another. Next, the exposed resist film 602 is developed as shown in FIG. 28(c), to form a plurality of angled convex portions 606a and 606b whose heights are different from each other. And then, as shown in FIG. 28(d), the angled convex portions 606a and 606b are heated to soften the angled parts of the convex portions 606a and 606b, with the result that rounded concave portions 608a and 608b are formed. Subsequently, a predetermined amount of polymer resin 620 is filled up in pitches 610 between the concave and convex portions to form a continuous layer having a wavelike surface, as shown in FIG. 28(e). Finally, a continuous wavelike reflecting electrode 624 is formed on the polymer resin film 620 using a laminating method, for example, a sputtering method.
In the reflection type liquid crystal display device or the hybrid reflecting/transmitting type liquid crystal display device disclosed in Japanese Unexamined Patent Application Publication No. 6-27481 etc., however, a plurality of concave and convex portions whose heights are different from one another are provided using a mask having a plurality of circles whose diameters are different from one another and which are regularly arranged or partially irregularly arranged, by means of ultraviolet exposure and development, so that it is difficult to adjust the heights precisely since the coating thickness is not uniform, whereby the light interference is not effectively prevented. Furthermore, electric lines may be easily broken or short-circuited because the reflecting electrode is formed on a plurality of concave and convex portions whose heights are different from one another. Also, a method for manufacturing the disclosed substrate with the light reflecting film has drawbacks in that it comprises too many steps, and thus involves control of many items.
Consequently, it is difficult to effectively prevent the generation of the interference fringes in the substrates with the light reflecting film disclosed in Japanese Unexamined Patent Application Publication No. 6-27481, and it is difficult to manufacture the aforesaid substrate with the light reflecting film stably and efficiently.
Therefore, the inventors of the present invention examine thoroughly the aforesaid problems, and come to the conclusion that a substrate with a light reflecting film which reduces the occurrence of interference fringes can be easily obtained by the steps of forming a plurality of concave portions or convex portions on a base of the substrate with the light reflecting film, and randomly arranging the concave portions or the convex portions over a plane while the depths of the concave portions or the heights of the convex portions are substantially unchanged.
Therefore, it is an object of the present invention to provide a mask for easily manufacturing a substrate with a light reflecting film which reduces the occurrence of interference fringes, such substrate with a light reflecting film, a method for forming such light reflecting film, an electro-optical device comprising such substrate with a light reflecting film, and an electronic apparatus comprising such substrate with a light reflecting film.